Heavy duty truck tires with a relatively thick tread region cross-section typically experience a significant heat build up and a corresponding increase in operating temperature as the truck tire is being used on an associated vehicle.
Such heavy duty tire internal heat buildup under heavy loads is considered herein to be significantly different from internal heat buildup generated in high performance light duty tires (e.g. passenger automobile tire and light duty truck tires). Heat build up in a heavy duty tire tread (e.g. heavy duty truck tire tread) during the working of such heavy duty tires under load can be of sufficient magnitude to cause such heavy duty tires to operate at relatively high temperatures and thereby have an impact upon their long term heat durability.
For this invention, it is proposed to provide at least one transition rubber layer of at least one silica-rich, cis 1,4-polyisoprene rubber based composition positioned between the heavy duty tire tread cap layer and underlying circumferential belt plies to promote low hysteresis to reduce heat generation and thereby promote an associated long term durability, to promote adhesion of the transition rubber layer and adjoining rubber layers and also to promote tear resistance of the transition rubber layer.
Further, by way of providing such transition rubber in a form of a silica-rich rubber composition, the transition rubber layer in the heavy duty tire may be of a color which contrasts with the black color of adjoining carbon black reinforced, diene-based elastomer based tire components when said transition layer contains only a minimal amount of carbon black reinforcement, if any, and contains a colorant.
In one aspect, the heavy duty tire of this invention is required to be a tire having a minimum load bearing capacity of 4,000 pounds (1814 kg) and therefore is considered herein to be differentiated from a light duty tire having a maximum load bearing capacity of 3,500 (1587 kg), preferably a maximum load bearing capacity of 3,000 pounds (1361 kg). Reference: The Tire and Rim Association Handbook. 
The term “phr” where used herein means “parts per weight of a specified material per 100 parts by weight rubber, or elastomer, in a rubber composition”.